1. Field of the Invention
The present invention relates to a crown control method for a multi-roll rolling mill.
2. Description of the Prior Art
As a multi-roll rolling mill of this kind, a 12-high rolling mill, for example, as shown in FIGS. 6 and 7, has been heretofore known. An upper roll housing 1 supporting a group of upper rolls is vertically movably fitted in four posts 3 stood upright on a lower roll housing 2 supporting a group of lower rolls, and the group of upper rolls is screwed down by driving a worm wheel 8 meshed with said posts 3 by a screw-down motor 4 provided on the upper roll housing 1 through a worm 5, a worm wheel 6, a shaft 7 and a worm (not shown). The groups of upper and lower rolls each comprise work rolls 9, 10, two sets of intermediate rolls 11, 12 supporting said work rolls, and three sets of support rolls 13(b), 13(a), 13(c) supporting said intermediate rolls. Between each saddle 15 of a support roll 13(b) on inlet and outlet sides of the rolling mill and the upper roll housing 1 are formed a pair of wedge blocks 16, 17 for each saddle 15, wedge block 17 being vertically moved through a driving shaft 19 by means of a plurality of driving means 18 provided on the upper roll housing 1. This vertical movement of the wedge block 17 causes a fine adjustment of displacement of the saddles to control crowns of the work rolls 9, 10.
In the above-described 12-high rolling mill, an operator judges a mechanical crown amount applied to the work rolls while observing a plate shape on the outlet side of the rolling mill, and suitably manually drives the driving means 18 which vertically move the wedge block 17 to thereby adjust the crown of the work rolls.
However, recently, with the requirement of higher precision in the shapes of products and with the requirement of high productivity resulting from an increase in demand, the rolling speed is inevitably increased in speed. However, in the crown adjustment done by hand in the prior art, it is difficult not only to provide higher precision shapes but to maintain such precision. Indeed, it is impossible to cope, particularly, with a variation in shape of plate due to an acute variation of a thermal crown at the time of acceleration and deceleration. This yield is so poor as to deteriorate productivity.